Electrically operated disc brake with back-off protector

ABSTRACT

The electrically operated disc brake (10, 110, 310, 410) may be operated by either hydraulic pressure and an electric motor or operated solely by means of an electric motor. The electric motor (40, 340, 440) drives a sun gear (52, 352, 452) of a planetary gear assembly (50, 150, 350, 450). The planetary gear assembly (50, 150, 350, 450) includes a fixed ring gear (70, 370, 470) and a rotatable ring gear (80, 180, 380, 480), the rotatable ring gear (80, 180, 380, 480) having fewer teeth than the fixed ring gear (70, 370, 470) so that rotation of the planetary gears (54, 56, 58) effects a slower rate of rotation of the rotatable ring gear (80, 180, 380, 480). The rotatable ring gear (80, 180, 380, 480) engages a screw (88, 188, 388, 488) which is connected with the piston (30, 130, 330, 430). The piston (30, 330, 430) may be displaced by hydraulic fluid for a service application and the electric motor (40, 340, 440) utilized for a parking application. Alternatively, the piston (130) may be displaced by the electric motor (40) for both service and parking brake applications.

This application is a continuation-in-part of application Ser. No. 946,400 filed on Dec. 23, 1986.

This invention relates generally to a disc brake that may be operated both hydraulically and electrically, or solely by motor means.

Disc brakes have been utilized for many years in passenger cars, heavy duty trucks, and aircraft. Because of the increasing emphasis on reducing the weight of vehicles and simplifying the components thereof, it is desirable to develop a braking system that is operated electrically. Such a braking system must be highly reliable, cost effective, and practical within the packaging constraints of the particular vehicle. The present invention provides a disc brake that may be operated either solely by means of an electrically or hydraulically operated motor or be operated hydraulically for a service brake application and operated by the motor for a parking brake application. The result is a highly reliable, low cost, electrically operated disc brake which will fit readily within the packaging constraints of several vehicles.

The present invention comprises a disc brake that may be operated by motor means, comprising a caliper having a bore with a piston slidably received therein, the caliper and piston actuable to displace a pair of friction elements into engagement with a rotor, a planetary gear assembly disposed within said bore and comprising a sun gear, planetary gears, and a pair of ring gears, and the motor means coupled with said sun gear which drives the planetary gears, one ring gear fixed to said caliper and the other ring gear rotatable by said planetary gears, the other ring gear engaging screw means which is connected with said piston, operation of said motor means causing rotation of said other ring gear and operative displacement of said piston into engagement with one of said friction elements so that the caliper, by reaction, displaces the other friction element into engagement with said rotor.

The invention is described in detail below with reference to the drawings which illustrate embodiments in

FIG. 1 is a section view of the first embodiment;

FIG. 2 is a partial section view along view line 2--2 of FIG. 1;

FIG. 3 is a section view along view line 3--3 of FIG. 1;

FIG. 4 is a section view along view line 4--4 of FIG. 1;

FIG. 5 is a section view along view ling 5--5 of FIG. 1;

FIG. 6 is a section view of a second embodiment of an electrically operated disc brake;

FIG. 7 is an alternative embodiment of the brake of FIG. 6;

FIG. 8 is an end view of a duplex support plate and disc brake;

FIG. 9 is a section view of a twin bore disc brake;

FIG. 10 is a section view taken along view line 10--10 of FIG. 9;

FIG. 11 is an end view of the brake of FIG. 9;

FIG. 12 is a section view of a twin bore disc brake;

FIG. 13 is an end view of the brake of FIG. 12; and

FIG. 14 is a section view of the brake of the present invention having a back-off protector.

The disc brake of the present invention is referenced generally by numeral 10 in FIG. 1. Disc brake 10 comprises a brake that is operated by either hydraulic pressure or an electric motor. Disc brake 10 includes a caliper 12 having a caliper housing 14 with a bore 16. Caliper 12 extends over a pair of friction elements 18 and 20 which may be displaced toward one another in order to brake a rotor 22. The bore 16 comprises a stepped bore having a piston 30 slidably disposed therein, the piston having a seal 32 located thereabout in order to prevent hydraulic fluid from exiting bore 16. Caliper housing 14 is connected with an electric motor housing 24 which has a bore 26 housing an electric motor 40. Motor 40 may comprise other types of motors, such as an hydraulic motor. Housing 24 is coupled to caliper housing 14 by means of a clamp band 43, the clamp band 43 held together by a nut and bolt connection 44 (see FIG. 2). A planetary gear assembly 50 is disposed within bore 16, the planetary gear assembly 50 comprising a sun gear 52, three planetary gears 54, 56, and 58 (see FIG. 3), a two-part carrier 60 comprising carrier parts 61 and 62, pins 63 which carry the planetary gears, and two ring gears 70 and 80. Each ring gear has internal teeth, and ring gear 80 is rotatable but has fewer teeth than ring gear 70 which is fixed to caliper housing 14. Rotatable ring gear 80 includes thereabout a pair of seals 84, the seals preventing hydraulic fluid from entering into the planetary gear assembly. Rotatable ring gear 80 is coupled nonrotatably through a tapered spline connection 86 with screw means 88. Screw means 88 has external threads engaging the threads of nut 90, and is supported in opening 31 of piston 30 (see FIGS. 1 and 5). Nut 90 is coupled nonrotatably through a key connection 92 (see FIG. 4) with piston 30. Piston 30 is coupled nonrotatably by means of connection 93 with friction element 18. Disposed about screw means 88 is a screw-retaining plate 89 which is held in axial position between housing shoulder 15 and rotatable ring gear 80, the retaining plate 89 having a central opening 91 for screw means 88. Fixedly positioned retaining plate 89 prevents screw means 88 from moving axially within bore 16. Located at the other end of bore 16 is a motor plate 100 that encloses the end of bore 16 and also engages the steel ring 102 of motor 40. Plate 100 has an opening 103 which effects alignment of the drive shaft of motor 40, and the plate also extends within steel ring 102 in order to position the motor. Steel plate 100 keeps gearbox oil from entering into bore 26 and motor 40.

The planetary gear assembly has a high reduction ratio which is achieved by having fewer internal teeth on rotatable ring gear 80 than on fixed ring gear 70. Sun gear 52 causes planet carrier 60 to rotate in the same direction as the sun gear, but at a reduced speed due to the fixed ring gear 70. The two ring gears 70 and 80 have different numbers of teeth, the difference being equal to the number of planetary gears, (normally two or three). Thus, as planet carrier 60 rotates, the planetary gear teeth engage with the adjacent teeth of the two ring gears 70 and 80, and for each rotation of the planet carrier 60, rotatable ring gear 80 advances by three teeth (for a design with three planetary gears) or two teeth (for a design with two planetary gears). Hence, the overall ratio of the gear train is the ratio of speed of the sun gear to the planet carrier multiplied by the number of teeth of the output rotatable ring gear divided by the number of planetary gears. A typical system might have 18 teeth on the sun; 72 teeth on the fixed ring; 69 teeth on the output rotatable ring, and three planetary gears. The overall ratio would be:

    (72/18+1)×69/3=115/1

The difference in tooth numbers is achieved by modifying the operating pressure angles of the internal teeth so that the gear with fewer teeth (preferably the rotatable ring gear 80) engages at a higher pressure angle than that with more teeth. The high pressure angle teeth can be generated with a standard 20° involute cutter working on an enlarged internal gear blank at the appropriate ratio.

The screw means 88 can have a friction reducing surface treatment in order to improve drive efficiency. However, for parking brake use it is essential to choose a drive screw which is irreversible so that the brake remains applied after the motor current is turned off. A reverse motor torque is used to release the brake.

A motor control circuit which controls motor torque (or current) is used. In a parking brake application, a hand lever with force feedback can be used to control a variable sensor such as a rheostat or force transducer which signals the controller to provide the appropriate motor current. Alternatively, a parking switch can activate the brake and an inclination sensor can provide a motor current level more than adequate for the grade, with a fully laden vehicle. With either system (and unlike a spring brake), the motor is controlled to provide enough torque to park the vehicle, without using unnecessarily high torques which load the mechanism excessively. Also, because current is proportional to torque, when the brake is applied for a parking brake application a datum point may be set when a predetermined force level is reached, and this datum point would be utilized by the controller during the release of the brake. Brake release would be accomplished by reversing the motor, but in order to maintain proper brake adjustment, the motor should be stopped when a small brake pad clearance is reached. To do this, the motor controller senses a predetermined low level current at the datum, during backoff, then continues turning the motor for a desired number of motor turns, which creates the necessary pad clearance.

Drive shaft flat 42 (see FIGS. 1 and 6) permits the attachment of a hand crank so that the brake can be applied or released manually.

Turning now to FIG. 6, there is illustrated an electrically operated disc brake 110 which utilizes an electric motor for both service and parking brake applications. Similar structure will be indicated by the same numerals utilized above. The caliper housing 114 includes a stepped bore 116, the stepped bore having a radially extending wall 118 which extends to an opening 119 that provides journalling for the output shaft of the electric motor 40. The planetary gear system 150 includes a fixed ring gear 70 and a rotatable ring gear 180. The rotatable ring gear 180 has fewer teeth than the fixed ring gear 70. Rotatable ring gear 180 includes a seal 84 disposed thereabout and gear 180 engages a ring 85 extending radially inwardly of stepped bore 116. Piston 130 is disposed at the entrance of stepped bore 116 and is positioned on rotatable ring gear 180. Another seal 184 is disposed about rotatable ring gear 180 and engages the interior surface of opening 131 of piston 130. Rotatable ring gear 180 engages screw means 188 by means of internal ring gear threads 185 and screw means threads 189. Screw means 188 is fixed nonrotatably through a key connection 190 with piston 130. Piston 130 is fixed nonrotatably by a key connection 192 with the inner friction element 118. In this embodiment of the invention, the rotatable ring gear 180 engages directly screw means 188 which is fixed nonrotatably with the piston that is fixed to the nonrotatable friction element 118. Thus, as rotatable ring gear 180 rotates, screw means 188 is displaced axially to engage friction element 118 with rotor 22, and by reaction, friction element 120 with the other side of rotor 22. The caliper housing 114 has an extension 124 which houses the electric motor 40. Because rotatable ring 180 engages directly screw means 188 which is fixed nonrotatably to piston 130, that portion of the structure is substantially shortened axially in relation to the previous embodiment. This enables electric motor 40 to be housed directly within extension 124 of caliper housing 114, the overall length of electric brake 110 being shortened. Electrically operated disc brake 110 has a planetary gear system which operates identically to that described above, but does not utilize any hydraulic pressure to actuate piston 130. Piston 130 is actuated both for service brake and parking brake applications by electric motor 40. In all other respects, electric disc brake 110 operates as described above for the first embodiment. FIG. 7 illustrates an alternative piston-screw means-rotatable ring gear structure. Screw means 288 is connected nonrotatably by spline connection 286 with rotatable ring gear 280, and screw means threads 289 engage piston threads 285 of piston 230.

The disc brake of FIG. 6 may be utilized for a parking brake application and a separate hydraulic disc brake utilized for service brake applications. FIG. 8 illustrates a duplex support plate 300 which supports both the electric disc brake 110 and a separate hydraulically operated disc brake 400 (both shown in dotted line outlines).

FIG. 9 illustrates a twin bore disc brake 310 having a pair of disc brake mechanisms disposed within twin bores and actuated by an electric motor disposed adjacent or parallel to the bores of the actuators. Twin bore disc brake 310 includes a caliper 312 which engages outer friction element 320, caliper housing 314 having bores 316 receiving therein pistons 330. Each piston 330 is displaced either by pressurized hydraulic brake fluid or by the electric motor 340 via the planetary gear assembly 350. Each piston 330 engages the inner brake pad 318 disposed adjacent rotor 322, piston 330 receiving nonrotatably by means of a key connection the nut 390 engaging the screw means 388. Piston 330 engages non-rotatably by means of key connection 393 the friction element 318. Each planetary gear assembly 350 is identical to those described above, in that it includes a non-rotatable ring gear 370 disposed coaxially with the rotatable ring gear 380, the gear assembly 350 including a sun gear 352 which drives three planatary gears. Sun gear 352 is connected with gear 351 that is engaged by idler 353 (see FIG. 10). The electric motor 340 is disposed parallel to the axis of bore 316, and includes a drive shaft 341 with drive gear 345 that powers idler 353. Idler 353 drives the two gears 351 each of which is connected via a shaft with an associated sun gear. FIG. 10 illustrates an end section view of the disc brake 310, and each bore of the twin bore disc brake includes a planetary gear assembly 350 and other structure identical to that shown in FIG. 9. Disc brake 310 includes an outer end plastic housing cover 317 which is held in place by clamp bracket 321 (see FIG. 11). Clamp bracket 321 includes legs 323 which hold housing cover 317 in place. As shown by FIG. 9, caliper housing 314 includes end portion 315 which is integral with the remaining portions of caliper housing 314 so that the Planetary gear assemblies 350 and pistons 330 are both enclosed within the bores 316. The outer diameter of the planetary gear assemblies 350 located within the twin bores of disc brake 310 are essentially the same as the outer piston diameters. Thus, the gear assemblies 350 are small enough to be housed within bores 316 and provide the required actuation loads while permitting the utilization of an integral caliper housing which is disposed about the ends of gear assemblies 350 in order to receive the reaction loading or forces effected by assemblies 350 when they operate and displace pistons 330 outwardly against rotor 322.

FIGS. 12 and 13 represent an embodiment which comprises a twin bore disc brake 410 having one piston actuated solely by means of hydraulic fluid pressure and the other piston actuated by either hydraulic fluid pressure or by means of a planetary gear assembly 450 actuated by an electric motor 440 disposed parallel to the twin bores. Structure similar to that described above is identified by the same numeral increased by 100. Disc brake 410 comprises a right side bore 416 housing the piston 430, screw means 488, nut 490, and planetary gear assembly 450. The left side bore 428 (see FIG. 13) includes a typical disc brake piston (not shown) which is actuated or displaced solely by pressurized brake fluid. The electric motor 440 is disposed upon an axis located parallel to the longitudinal axis of disc brake 410, and includes a motor shaft 441 connected to a drive gear 445 which drives the idler 453 that engages gear 451 connected with sun gear 452. As a result, the left side bore 428 (see FIG. 13) containing the hydraulically actuated piston may be utilized for service brake applications, while the right side bore 416 containing the planetary gear assembly 450 may be actuated by electric motor 440 via idler 453 for parking brake applications and actuated hydraulically for service brake applications.

Referring now to FIG. 14, there is illustrated an electrically operated disc brake 510 which utilizes an electric motor for both service and parking brake applications. Similar structure will be indicated by the same reference numerals utilized above. The caliper housing 114 includes a stepped bore 116, the stepped bore providing support for an electric motor 40. The planetary gear system 150 includes a fixed ring gear 570 and a rotatable ring gear 580. The rotatable ring gear 580 has fewer teeth than the fixed ring gear 570. Rotatable ring gear 580 includes a seal 584 disposed thereabout and gear 580 engages a ring 583 extending radially and axially inwardly of stepped bore 116. A piston or nut 530 is disposed at the entrance of stepped bore 116 and is positioned on screw means 588 connected non-rotatably with rotatable ring gear 50. Rotatable ring gear 580 includes an axial recess 581 which includes peripheral radial slots 582. Screw means 588 comprises a radial flange 586 which is received non-rotatably within the radial slots 582 of recess 581. Screw means threads 589 engage nut threads 585 of nut 530. Nut 530 engages a backing plate 192 of friction element 118. Disposed about screw flange 586 is a rubber or resilient disc 587, the disc 587 providing a resilient surface for engagement by the nut 530 when the nut translates to the right in FIG. 14, during release of the brake.

Non-rotatable ring gear 570 includes a radial recess 571 which receives a rubber or resilient ring member 572. The resilient member 572 may, alternatively, comprise a spring clutch 573. Both the rubber ring 572 and spring clutch 573 provide low rotational friction for the fixed ring gear when the disc brake operates to reverse or release the nut 530. However, during operation of brake 510 to effect braking by application of the nut 530 against friction element 118, the reaction forces through the brake effect a very high frictional force between fixed ring gear 570, resilient member 572 or clutch 573, and the surface of stepped bore 116.

When brake 510 is operated to apply friction element 118 against rotor 22, the axial thrust effected by nut 530 against friction element 118 and rotor 22, coupled with the application of friction element 120 against rotor 22, effects a substantial axial thrust through the planetary gear assembly so that the ring gear 570 effects substantial frictional engagement with the stepped bore 116 and will not rotate relative thereto. In other words, ring gear 570 becomes fixed relative to housing 114 during the application operation of brake 510. However, when the brake 510 is operating to release friction elements 118, 120 from engagement with rotor 22, nut 530 moves along screw means 588 toward the right in FIG. 14, and toward planetary gear assembly 150. If motor 40 is not stopped before nut 530 reaches the end of screw means thread 589, the engagement of nut 530 with rotatable ring gear 580 may cause damage to the assembly 150 or nut 530 may become jammed against rotatable ring gear 580. In order to prevent mechanical damage, ring gear 570 is permitted to rotate relative to housing 114 during the release phase of braking. During the release phase of braking, there is essentially no axial load reaction through planetary gear assembly 150. During the release of braking, the presence of resilient rubber ring 572 or spring clutch 573 provides a small frictional resistance which may be overcome easily by the torque imposed upon ring gear 570. This small residual friction effected by resilient member 572 or clutch 573 permits friction elements 118, 120 to be backed off, by means of motor 40, so that they are clear of rotor 22, and if the release phase of braking results in nut 530 being backed off to the extent that it engages the rubber disc 587 and flange 586 of screw means 588 which is fixed non-rotatably to rotatable ring member 580, then back-off torque effected through planetary gear assembly 150 will cause ring gear 570 to rotate relative to housing 114. This prevents any damage being caused by the back-off of nut 530. The rubber disc 587 is mounted on screw means 588 in order to prevent hard contact of nut 530 against the flange 586, and other mechanical stops may be utilized therefor. Rubber disc 587 insures that nut 530 will then be able to drive forward (in the leftward direction) when the rotation of screw means 588 is reversed for the application phase of braking.

The back-off protector of disc brake 510 provides substantial advantages during the operation of the brake. Any possible damage to brake 510, and in particular the planetary assembly 150, is avoided because excessive back-off is eliminated. A less sophisticated motor controller is required because the mechanical structure of brake 510 compensates for any excessive back-off of nut 530. Also, the need to use closely controlled dimensions on the outside of ring gear 570 and for bore 116 of housing 114 is eliminated, because resilient member 572 or clutch 573 positions centrally the ring gear 570. This effects substantial cost savings between the two components which more than offsets the costs of adding two rubber parts or a coil spring to the brake. Of course, the back-off protector prevents the nut 530 from jamming against its stop comprising flange 586, so that the brake 510 can be reapplied and effect braking of rotor 22.

The various embodiments of the disc brake having the planetary gear assembly may be utilized for drive line braking of a vehicle. The "rotor" to be braked may be attached to the vehicle's propulsion shaft or driven by it, and the caliper mounted on the transmission or rear axle assembly. All of the above-described motors may be electric motors, hydraulic motors, and any other appropriate driving source.

Other provisions of the invention or variations will become apparent to those skilled in the art and will suggest themselves from the specific applications of the invention. It is intended that such variations and revisions of the invention as reasonably to be expected on the part of those skilled in the art, to suit individual design preference and which incorporate the herein disclosed principles, will be included within the scope of the following claims as equivalents thereof. 

We claim:
 1. A disc brake that may be operated by motor means, comprising a caliper having a bore with a nut disposed at an end thereof, the caliper and nut actuatable to displace a pair of friction elements into engagement with a rotor, a planetary gear assembly disposed within said bore and comprising a sun gear, planetary gears, and a pair of ring gears, and motor means coupled with said sun gear which drives the planetary gears, one ring gear frictionally engaging the bore of said caliper and the other ring gear rotatable by said planetary gears, the other ring gear engaging nonrotatably screw means which is connected with said nut, operation of said motor means causing rotation of said other ring gear and displacement of said nut into engagement with one of said friction elements so that the caliper, by reaction, displaces the other friction element into engagement with said rotor, the one ring gear having resilient means disposed thereat between the one ring gear and the bore of the caliper, the resilient means effecting in one direction of rotation of the other ring gear a low frictional engagement between said one ring gear and bore and in another direction of rotation of said other ring gear a high frictional engagement between said one ring gear and bore, whereby rotation of said other ring gear in the one direction of rotation may cause the one ring gear to rotate relative to said housing.
 2. The disc brake in accordance with claim 1, wherein said nut may translate along said screw means and engage an end of said screw means which may cause said other ring gear to effect, by reaction therethrough, said rotation of the one ring gear relative to the housing.
 3. The disc brake in accordance with claim 2, wherein the one ring gear includes a radial recess with the resilient means disposed therein.
 4. The disc brake in accordance with claim 3, wherein the other ring gear includes a axial recess having slot means thereat, the screw means having a flange which is received within the slot means to effect the nonrotatable connection of the screw means with the other ring gear.
 5. The disc brake in accordance with claim 4, wherein a resilient member is disposed adjacent the flange of the screw means, the nut engageable with the resilient member during said translation of the nut along the screw means.
 6. The disc brake in accordance with claim 3, wherein the resilient means disposed within the radial recess of the one ring gear comprises a rubber ring.
 7. The disc brake in accordance with claim 3, wherein the resilient means disposed within the radial recess of the one ring gear comprises a coil clutch spring. 